Herbicides eliminate unwanted weeds in the garden. Weeds compete for available resources such as soil nutrients, sunlight and water. Weeds are unsightly in a flower garden and they impede growth in the vegetable garden. Traditional herbicides are produced from synthetic chemicals; newer concepts of weed control make use of nontoxic herbicides, cultural controls, cover crops, mulch and handpicking methods. Preparation for weed control using herbicides and other methods begins in early planting season.
Glyphosate, the primary ingredient (40 percent of content) in Roundup, is the most used herbicide globally. It was introduced by the Monsanto company in 1974 and has become the first herbicide to be identified as causing reproductive abnormalities in laboratory testing. Herbicides are classified as pesticides by the EPA. Health risks depend on the type of herbicide. Corn gluten meal pre-emergent herbicide does not pose a health risk, but glyphosate products pose risks to women in their reproductive years. Home gardeners are encouraged to read labels carefully and use the EPA website for product risk assessments.
Contact herbicides destroy only the plant tissue that comes in contact with the product.They include Scythe and Bayer Advanced All-in-One Weed Killer. These are less effective on perennial plants that re-grow from tubers, bulbs and roots. Systemic herbicides are absorbed by the plant and cause cell death from within. They are effective on perennial weeds but work more slowly than contact herbicides.Examples of systemic weed killer include Roundup and Ortho Weed-B-Gone. Organic herbicides are produced from spices, vinegars and concentrated natural oils such as neem and citrus. Pre-emergent herbicides such as Orland's Safe-t-Weed prevent weeds from germinating.They require rainfall or watering to be effective.
Toxic synthetic herbicides and organic natural-source herbicides are applied by a hand-held sprayer in home garden use. Products are hand-mixed and poured into a sprayer. Pre-emergent herbicides are hand-broadcast over lawn turf in early spring or fall when weeds germinate. The area must be kept moist for product effectiveness. Care should be taken when spraying contact synthetic herbicides so the chemicals do not touch landscape plantings. Spray directly onto weeds only.
Tall plants in the vegetable garden such as squash, corn, tomatoes, cucumbers and melons suppress weed growth by shading. It works best when tall plants germinate and grow quickly, suppressing weeds that need sunlight. Mulch layers in the flower or vegetable garden help to eliminate weed germination or suppress weed growth by smothering them. Mulch materials such as aged compost, old newspapers or brown paper bags, shredded bark or dried leaves decompose over time and add organic matter to the soil.
Cover crops are used in large agricultural crops as well as home gardens to suppress weeds and improve soil health. Legume plants such as clover and field peas absorb nitrogen from the air and translocate it to roots and soil. Nitrogen is the element that requires renewal most often by growing plants. When peas are broadcast thickly around rose beds in the winter they suppress weeds and provide mulch as their growth cycle comes to completion in spring.
The "inert ingredients" in synthetic chemical herbicide products are considered trade secrets by the EPA, and listing them is not required by law. It is the unlisted ingredients in glyphosate formulas that have been linked to extreme toxicity, in laboratory testing, according to a study reported in the June 2005 issue of "Environmental Health Perspectives." There is a synergistic effect between glyphosate and the product's surfactants which is thought to cause cell abnormalities to develop. Read all warning labels before using herbicides in gardens where there are pets, children, vulnerable elders or sensitive wildlife such as butterflies and beneficial insects.